Optical fiber

ABSTRACT

An optical fiber includes a glass portion, a primary coating layer, and a secondary coating layer. In the optical fiber, a value of microbend loss characteristic factor F μBL_GO  is 2.6 ([GPa −1 ·μm −10.5 ·dB/turn]·10 −27 ) or less, when represented by
 
 F   μBL_GO   =F   μBL_G   ×F   μBL_O  
 
by using geometry microbend loss characteristic F μBL_G  and optical microbend loss characteristic F μBL_O .

TECHNICAL FIELD

The present invention relates to an optical fiber, specifically, to anoptical fiber that can be used for an optical fiber cable.

BACKGROUND

In recent years, the traffic of communication infrastructuresconstructed by optical fiber cables and the like has been increasing dueto the maturity of Fiber To The Home (FTTH) services, the spread ofmobile terminals, the expansion of cloud service usage, the increase invideo traffic, and the like. Therefore, it is demanded to constructcommunication infrastructures more economically and efficiently thanbefore. Under such background, there is a demand to increase the numberof mounting cores and mounting density of optical fibers mounted inoptical fiber cables.

As a means for increasing the number of mounting cores and mountingdensity of the optical fibers, it is conceivable to reduce the diameterof the optical fibers. However, in this case, the optical fibers areeasily affected by the lateral pressure, and the microbend loss, whichis the optical loss caused by the shaft of the optical fibers beingslightly bent, can be large. Patent Literature 1 below describes thatthe elastic modulus and the glass transition point of an optical fibercoating are adjusted to reduce the coating thickness of the opticalfiber so that the microbend loss can be suppressed even when thediameter of the optical fiber is reduced.

PATENT LITERATURE

[Patent Literature 1] JP 2012-508395 A

However, the aforementioned microbend loss tends to be affected byparameters related to the geometry of the optical fiber such as thecoating thickness of the optical fiber, the outside diameter of theglass forming the core and the clad, the Young's modulus of theaforementioned glass, and the Young's modulus of the coating, andparameters related to the optical characteristics of the optical fibersuch as the mode field diameter of light propagating through the opticalfiber, the cutoff wavelength, and the macrobend loss. In PatentLiterature 1 described above, the coating thickness is taken intoconsideration as the aforementioned parameter in terms of suppressingmicrobend loss, but the parameters other than the coating thickness arenot taken into consideration. Therefore, there is a demand for anoptical fiber capable of suppressing microbend loss that takes intoconsideration various parameters that affect microbend loss.

SUMMARY

One or more embodiments of the invention provide an optical fibercapable of suppressing microbend loss.

An optical fiber according to one or more embodiments includes a glassportion including a core and a clad surrounding the core, a primarycoating layer covering the clad, and a secondary coating layer coveringthe primary coating layer, in which a value of microbend losscharacteristic factor F_(μBL_GO) [(GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷)represented byF _(μBL_GO) =F _(μBL_G) ×F _(μBL_O)

by using geometry microbend loss characteristic F_(μBL_G)(GPa⁻¹·μm^(−10.5)·10⁻²⁷) of the optical fiber represented by

$\mspace{20mu}{F_{\mu\;{BL}\;\_\; G} = \frac{K_{S}^{2}}{H_{f}^{2} \times D_{0}^{0.375} \times H_{0}^{0.625}}}$${K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {R_{s}^{4} - R_{p}^{4}} \right)}}}$

when a spring coefficient of the primary coating layer is κs (MPa), abending rigidity of the glass portion is H_(f) (MPa·μm⁴), a deformationresistance of the secondary coating layer is D₀ (MPa), a bendingrigidity of the secondary coating layer is H₀ (MPa·μm⁴), a Young'smodulus of the glass portion is E_(g) (GPa), a Young's modulus of theprimary coating layer is E_(p) (MPa), a Young's modulus of the secondarycoating layer is E_(s) (MPa), an outside diameter of the glass portionis d_(f) (μm), a radius of an outer peripheral surface of the primarycoating layer is R_(p) (μm), a radius of an outer peripheral surface ofthe secondary coating layer is R_(s) (μm), a thickness of the primarycoating layer is t_(p) (μm), and a thickness of the secondary coatinglayer is t_(s) (μm), and optical microbend loss characteristic F_(μBL_O)(dB/turn) of the optical fiber represented by

$F_{\mu\;{BL}\;\_\; O} = {\frac{2w}{\lambda_{cc}} \times \alpha_{BL}}$

when a mode field diameter of light having a wavelength of 1310 nmpropagating through the optical fiber is 2w (μm), a cutoff wavelength ofthe optical fiber is λ_(cc) (μm), and a macrobend loss of the opticalfiber at a wavelength of 1625 nm and a radius of 10 mm is α_(BL)(dB/turn), is 2.6 or less.

The microbend loss of optical fiber is, as described in Non-PatentLiterature 1 (J. Baldauf, et al., “Relationship of MechanicalCharacteristics of Dual Coated Single Mode Optical Fibers andMicrobending Loss, “IEICE Trans. Commun., vol. E76-B, No. 4, 1993) andNon-Patent Literature 2 (C. Unger, et al., “Characterization of thebending sensitivity of fibers by the MAC-value, “Optics Communicationsvol. 107, no. 5-6, pp. 361-364, 1994), tends to be affected by both thegeometry and the optical characteristics of the optical fiber.

Here, the geometry of the optical fiber is a parameter related to thestructure of the optical fiber, and, in one or more embodiments of theinvention, the spring coefficient κs of a primary coating layer of theoptical fiber, the bending rigidity H_(f) of a glass portion, thedeformation resistance D₀ of a secondary coating layer, the bendingrigidity H₀ of the secondary coating layer, the Young's modulus E_(g) ofthe glass portion, the Young's modulus E_(p) of the primary coatinglayer, the Young's modulus E_(s) of the secondary coating layer, theoutside diameter d_(f) of the glass portion (diameter of the glassportion), the radius R_(p) of the primary coating layer, the radiusR_(s) of the secondary coating layer, the thickness t_(p) of the primarycoating layer, and the thickness t_(s) of the secondary coating layer.

Furthermore, the optical characteristics of the optical fiber areparameters related to the characteristics of the light propagatingthrough the optical fiber, and are, in one or more embodiments of theinvention, the mode field diameter 2w of the light propagating throughthe optical fiber, the cutoff wavelength λ_(cc) of the optical fiber,and the macrobend loss (bending loss) α_(BL) of the optical fiber.

The microbend loss of such an optical fiber may be represented by thevalue of sandpaper tension winding loss increase, which is thedifference between the transmission loss measured in a state where theoptical fiber is wound in one layer with a predetermined tension on aroughened bobbin body portion and the transmission loss measured in astate where the optical fiber is unwound from the bobbin with almost notension applied. The smaller the value of such sandpaper tension windingloss increase becomes, the smaller is the microbend loss of the opticalfiber.

By the way, as an optical fiber cable constituting communicationinfrastructures, a so-called tape slot type cable (RSCC: Ribbon SlottedCore Cable) including a plurality of tape core wires accommodated ineach of a plurality of slots formed on a holding body for holding thetape core wires and a small-diameter high-density cable (UHDC:Ultra-High Density Cable) including tape core wires densely arrangedinside the cable without using the aforementioned holding body areknown. Of these, since the tape slot type cable has a structure in whicha plurality of tape core wires are accommodated in the slots asdescribed above, a lateral pressure is applied to the optical fibersconstituting the tape core wires, which may cause microbend loss.Therefore, in the tape slot type cable, in consideration of suchmicrobend loss, an optical fiber may be used in which the value ofsandpaper tension winding loss increase is suppressed to 0.6 dB/km orless.

The relationship between the sandpaper tension winding loss increase andthe aforementioned various parameters regarding the optical fiber usedfor the optical fiber cable were studied. As a result, it was found thatthe value of microbend loss characteristic factor F_(μBL_GO) representedby the aforementioned formula has a high correlation with the value ofsandpaper tension winding loss increase. That is, the value of themicrobend loss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase.

Furthermore, when the value of the aforementioned microbend losscharacteristic factor is 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷), thevalue of the sandpaper tension winding loss increase is a value slightlysmaller than 0.6 dB/km. As described above, the value of the microbendloss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase. Therefore, by setting the value of the microbend losscharacteristic factor of the optical fiber to 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, the microbend loss can besuppressed to the extent that the optical fiber can be applied to thetape slot type cable.

As described above, with the optical fiber of one or more embodiments ofthe invention, the microbend loss can be suppressed.

Furthermore, the value of the microbend loss characteristic factor maybe 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less.

Among the optical fiber cables constituting the communicationinfrastructures, in the small-diameter high-density cable, the tape corewires are densely arranged as described above. Therefore, similar to thetape slot type cable, the optical fiber constituting the tape core wireis subjected to a lateral pressure, and the microbend loss can occur.Furthermore, since the small-diameter high-density cable is slotless asdescribed above and all the tape core wires are densely arranged insidethe cable, the optical fiber tends to be subjected to a large lateralpressure as compared with the tape slot type cable in which the tapecore wires are separately arranged in a plurality of grooves. Therefore,in the small-diameter high-density cable, it is recommended to use anoptical fiber having a smaller microbend loss than the optical fiberused for the tape slot type cable. In view of the above, in thesmall-diameter high-density cable, an optical fiber may be used in whichthe value of sandpaper tension winding loss increase is suppressed to0.34 dB/km or less.

The value of the microbend loss characteristic factor substantiallycorresponding to the value (0.34 dB/km) of the sandpaper tension windingloss increase is 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷). Therefore, bysetting the value of the microbend loss characteristic factor of theoptical fiber to 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, themicrobend loss can be suppressed to the extent that the optical fibercan also be applied to the small-diameter high-density cable.

Furthermore, in the aforementioned optical fiber, the coating thicknessof a sum of the thickness of the primary coating layer and the thicknessof the secondary coating layer may be 42.0 μm or less.

The larger the aforementioned coating thickness becomes, the larger theoutside diameter of the optical fiber tends to be, and the smaller thecoating thickness becomes, the smaller the outside diameter of theoptical fiber tends to be. The optical fiber used for the optical fibercable constituting the communication infrastructures generally has acoating thickness of approximately 60 μm. Therefore, when the coatingthickness is 42.0 μm or less, it is possible to realize an optical fiberhaving a smaller diameter than a general optical fiber constituting thecommunication infrastructures. By the way, the value of the microbendloss characteristic factor is determined by various parameters asdescribed above, and the parameters include the thickness of the primarycoating layer and the thickness of the secondary coating layer.Therefore, according to one or more embodiments of the invention, evenwhen the thickness of the primary coating layer or the thickness of thesecondary coating layer is reduced, the value of the microbend losscharacteristic factor can be 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) orless or can be 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less byadjusting other parameters. Therefore, even when the coating thicknessof the optical fiber in one or more embodiments of the invention is 42.0μm or less, the microbend loss can be suppressed to the extent that theoptical fiber can be used for the tape slot type cable or thesmall-diameter high-density cable.

Furthermore, the coating thickness may be 38.0 μm or less.

Furthermore, the coating thickness may be 36.5 μm or less.

Furthermore, the coating thickness may be 34.5 μm or less.

Furthermore, the coating thickness may be 34.0 μm or less.

By reducing the coating thickness in this way, the microbend loss can besuppressed to the extent that the optical fiber can be used for the tapeslot type cable or the small-diameter high-density cable, and an opticalfiber with a smaller diameter can be realized.

Furthermore, when the coating thickness is 42.0 μm or less, the outsidediameter of the glass portion may be 65 μm or more and 100 μm or less.

The larger the outside diameter of the aforementioned glass portionbecomes, the larger the outside diameter of the optical fiber tends tobe, and the smaller the outside diameter of the glass portion becomes,the smaller the outside diameter of the optical fiber tends to be. Theoptical fiber used for the optical fiber cable constituting thecommunication infrastructures is generally formed such that the outsidediameter of the glass portion is approximately 125 μm. Therefore, whenthe coating thickness is 42.0 μm or less and the outside diameter of theglass portion is 100 μm or less, it is possible to realize an opticalfiber having a smaller diameter than a general optical fiberconstituting the communication infrastructures. By the way, the value ofthe microbend loss characteristic factor is determined by variousparameters as described above, and the parameters include the coatingthickness and the outside diameter of the glass portion. Therefore,according to one or more embodiments of the invention, even when thecoating thickness is reduced and the outside diameter of the glassportion is reduced, the value of the microbend loss characteristicfactor can be 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less or can be1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less by adjusting otherparameters. Therefore, even when the coating thickness of the opticalfiber in one or more embodiments of the invention is 42.0 μm or less andthe outside diameter of the glass portion is 100 μm or less, themicrobend loss can be suppressed to the extent that the optical fibercan be used for the tape slot type cable or the small-diameterhigh-density cable.

Note that when the outside diameter of a glass portion havingbrittleness is as thin as approximately 65 μm, the mechanical bendingresistance of the optical fiber can be increased by the amount that thebrittle glass is thinned.

Furthermore, the outside diameter of the glass portion may be 90 μm orless.

Furthermore, the outside diameter of the glass portion may be 80 μm orless.

Furthermore, the outside diameter of the glass portion may be 75 μm orless.

Furthermore, the outside diameter of the glass portion may be 70 μm orless.

By reducing the outside diameter of the glass portion in this way, themicrobend loss can be suppressed to the extent that the optical fibercan be used for the tape slot type cable or the small-diameterhigh-density cable, and an optical fiber with a far smaller diameter canbe realized.

Furthermore, when the aforementioned coating thickness is 42.0 μm orless, the mode field diameter of light having a wavelength of 1310 nmmay be 7.6 μm or more and 8.7 μm or less, the cable cutoff wavelengthmay be 1260 nm or less, the zero dispersion wavelength may be 1300 nm ormore and 1324 nm or less, and the zero dispersion slope may be 0.073ps/km/nm or more and 0.092 ps/km/nm or less.

In this case, the macrobend loss of light having a wavelength of 1625 nmby bending at a radius of 10 mm may be 1.5 dB/turn or less.

Alternatively, the macrobend loss of light having a wavelength of 1625nm by bending at a radius of 10 mm may be 0.2 dB/turn or less.

Alternatively, the macrobend loss of light having a wavelength of 1625nm by bending at a radius of 10 mm may be 0.1 dB/turn or less.

As described above, according to one or more embodiments of theinvention, there is provided an optical fiber capable of suppressing themicrobend loss.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cableaccording to a first embodiment.

FIG. 2 is a perspective view schematically showing an example of anoptical fiber tape core wire included in the optical fiber cable shownin FIG. 1.

FIG. 3 is a diagram schematically showing a structure of a cross sectionperpendicular to the longitudinal direction of the optical fiberincluded in the optical fiber tape core wire shown in FIG. 2.

FIG. 4 is a diagram showing a structure of a cross section perpendicularto a longitudinal direction of an optical fiber cable according to asecond embodiment.

FIG. 5 is a diagram showing a relationship between a value of microbendloss characteristic factor and sandpaper tension winding loss increasein the optical fiber shown in FIG. 3.

DETAILED DESCRIPTION

Aspects for carrying out the optical fiber according to the presentinvention will be illustrated below together with the accompanyingdrawings. The embodiments illustrated below are for facilitating theunderstanding of the present invention, and are not for limiting theinterpretation of the present invention. The present invention can bechanged or modified from the embodiments below without departing fromthe spirit. Furthermore, in the present specification, the dimensions ofeach member may be exaggerated for ease of understanding.

First Embodiment

FIG. 1 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cable 1according to the first embodiment. As shown in FIG. 1, the optical fibercable 1 is a so-called tape slot type cable (RSCC: Ribbon Slotted CoreCable). The optical fiber cable 1 includes a sheath 3, a plurality oftape core wires 4, a holding body 5, and a tensile strength body 6 asmain configurations.

The sheath 3 is a tubular member and may be formed of a thermoplasticresin such as polyethylene. The aforementioned holding body 5 isaccommodated in the internal space of the sheath 3. In this way, thesheath 3 accommodates the holding body 5 inside and protects the holdingbody 5.

The holding body 5 is a member that holds the plurality of tape corewires 4. A plurality of slots 5S are formed on the holding body 5, andthe plurality of tape core wires 4 are accommodated in the slots 5S.Note that by increasing the number of tape core wires 4 accommodated inthe slots 5S, the number of cores of optical fiber included in theoptical fiber cable 1 can be increased.

In the present embodiment, the tensile strength body 6 is embedded inthe substantially center of the holding body in the cross-sectional viewof FIG. 1. Such tensile strength body 6 can suppress the tape core wires4 from being stretched more than necessary when tension is applied inthe longitudinal direction of the tape core wires 4.

FIG. 2 is a perspective view schematically showing an example of thetape core wire 4. As shown in FIG. 2, the tape core wire 4 of thepresent embodiment is a so-called intermittent adhesive type tape corewire. The tape core wire 4 has a configuration in which a plurality ofoptical fibers 10 are arranged along a direction perpendicular to thelongitudinal direction, and the arranged optical fibers 10 are adheredto each other. The tape core wire 4 includes adhesive portions 4A andsingle core portions 4B. The adhesive portion 4A is a portion whereadjacent optical fibers 10 are adhered to each other, and is providedintermittently at a constant pitch along the longitudinal direction. Thesingle core portion 4B is a portion located between the adhesiveportions 4A, and is a portion where the optical fibers 10 are notadhered to each other. With such a configuration, the tape core wire 4can be easily deformed, for example, twisted or bundled in asubstantially cylindrical shape. FIG. 1 schematically shows a state inwhich each tape core wire 4 is bundled.

Note that FIG. 2 shows an example in which the tape core wire 4 includesfour optical fibers 10, but this is an example. That is, the number ofoptical fibers 10 constituting the tape core wire 4 is not particularlylimited, and may be less than four or may be more than four. Forexample, the tape core wire 4 may include 12-core optical fibers 10.Furthermore, the tape core wire 4 is not limited to the intermittentadhesive type.

FIG. 3 is a diagram showing a structure of a cross section perpendicularto the longitudinal direction of the optical fiber 10 constituting thetape core wire 4. The optical fiber 10 of the present embodiment is asingle-mode optical fiber. As shown in FIG. 3, the optical fiber 10includes a core 11, a clad 12 that surrounds the core 11 without gaps, aprimary coating layer 14 that covers the clad 12, and a secondarycoating layer 15 that covers the primary coating layer 14 as the mainconfigurations. In the optical fiber 10, the clad 12 has a lowerrefractive index than the core 11.

The core 11 may be formed of pure quartz to which no dopant has beenadded, or may be formed of quartz to which germanium (Ge) or the likethat increases the refractive index has been added as a dopant.

The clad 12 has a lower refractive index than the core 11 as describedabove. For example, when the core 11 is formed of pure quartz, the clad12 may be formed of quartz to which fluorine (F), boron (B), or the likethat lowers the refractive index has been added as a dopant, and whenthe core 11 is formed of quartz to which germanium (Ge) or the like thatincreases the refractive index has been added as a dopant, the clad 12may be formed of pure quartz to which no dopant has been added.Furthermore, the clad 12 may be formed of quartz to which chlorine (Cl2)has been added. Furthermore, the clad 12 may be a single layer, mayinclude a plurality of layers having different refractive indexes, ormay be a hole-assisted type.

As described above, the core 11 and the clad 12 are both formed ofquartz (glass). Therefore, the core 11 and the clad 12 are collectivelyreferred to as a glass portion 13. That is, the glass portion 13includes the core 11 and the clad 12, and the glass portion 13 iscovered with the primary coating layer 14. Note that the glass portion13 is sometimes referred to as an optical fiber bare wire portion. Theoutside diameter (diameter) d_(f) of such glass portion 13 is generallyapproximately 125 μm. However, in the present embodiment, the outsidediameter d_(f) of the glass portion 13 can be a smaller outsidediameter. For example, it can be 65 μm or more and 100 μm or less, 65 μmor more and 90 μm or less, 65 μm or more and 80 μm or less, 65 μm ormore and 75 μm or less, or 65 μm or more and 70 μm or less. The reasonwhy the outside diameter d_(f) of the glass portion 13 can be small inthis way will be described later.

Note that when the outside diameter d_(f) of a glass portion havingbrittleness is as thin as approximately 65 μm, the mechanical bendingresistance of the optical fiber can be increased by the amount that thebrittle glass is thinned.

The primary coating layer 14 is formed of, for example, an ultravioletcurable resin or a thermosetting resin, and is formed on an outer sideof the glass portion 13 with a thickness t_(p) (μm). In the presentembodiment, the Young's modulus E_(g) of the primary coating layer 14 islower than the Young's modulus E_(s) of the secondary coating layer 15.By setting the primary coating layer 14 in direct contact with the glassportion to have a low Young's modulus in this way, the primary coatinglayer 14 acts as a cushioning material, and the external force acting onthe glass portion 13 can be reduced. Note that assuming that the radiusof the outer peripheral surface of the primary coating layer 14 is R_(p)(μm), the outside diameter of the primary coating layer 14 isrepresented by 2R_(p), and assuming that the radius (d_(f)×½) of theglass portion is R_(g) (μm), the aforementioned thickness t_(p) of theprimary coating layer 14 is represented by the formula described below.t _(p) =R _(p) −R _(g)

In the present embodiment, the secondary coating layer 15 is a layerforming the outermost layer of the optical fiber 10, and is formed of,for example, an ultraviolet curable resin or a thermosetting resindifferent from the type of resin forming the primary coating layer 14,and is formed on an outer side of the primary coating layer 14 with athickness t_(s) (μm). For example, when the primary coating layer 14 isformed of an ultraviolet curable resin, the secondary coating layer 15may be formed of an ultraviolet curable resin different from theultraviolet curable resin forming the primary coating layer 14, and whenthe primary coating layer 14 is formed of a thermosetting resin, thesecondary coating layer 15 may be formed of a thermosetting resindifferent from that of the primary coating layer 14. In the presentembodiment, the Young's modulus E_(s) of the secondary coating layer 15is higher than the Young's modulus E_(g) of the primary coating layer14. As described above, by setting the secondary coating layer 15forming the outermost layer of the optical fiber 10 to have a highYoung's modulus, the glass portion 13 can be appropriately protectedfrom the external force. Note that assuming that the radius of the outerperipheral surface of the secondary coating layer 15 is R_(s), theoutside diameter of the secondary coating layer 15, i.e., the outsidediameter of the optical fiber 10 is represented by 2R_(s), and theaforementioned thickness t_(s) of the secondary coating layer 15 isrepresented by the formula described below.t _(s) =R _(s) −R _(p)

By the way, the outside diameter of the optical fiber used for theoptical fiber cable is generally approximately 240 μm to 250 μm.Therefore, the outside diameter of the secondary coating layer 15 may beapproximately 240 μm. However, in the present embodiment, the outsidediameter of the secondary coating layer 15 can be smaller than 240 μm.For example, it can be approximately 190 μm, approximately 150 μm toapproximately 160 μm, or approximately 125 μm. The reason why theoutside diameter of the secondary coating layer 15, i.e., the outsidediameter of the optical fiber 10 can be small in this way will bedescribed later.

Furthermore, assuming that the sum of the thickness t_(p) of the primarycoating layer 14 and the thickness t_(s) of the secondary coating layer15 is the coating thickness t, the coating thickness of the opticalfiber used for the optical fiber cable is generally approximately 60 μm.Therefore, the coating thickness t of the optical fiber 10 may beapproximately 60 μm. However, in the present embodiment, the coatingthickness t of the optical fiber 10 can be smaller than 60 μm. Forexample, it can be 42.5 μm or less, 38.0 μm or less, 36.5 μm or less,34.5 μm or less, or 34.0 μm or less. The reason why the coatingthickness of the optical fiber 10 can be small in this way will bedescribed later.

As described above, in the optical fiber cable 1 of the presentembodiment, the tape core wires 4 including a plurality of such opticalfibers 10 are densely accommodated in the slots 5S of the holding body5. As a result, the optical fiber cable 1 can accommodate a large numberof cores of optical fiber. For example, the optical fiber cable 1accommodates 1000-core or more optical fibers. Furthermore, as describedabove, in the optical fiber 10 of the present embodiment, the glassportion 13 can be formed to have an outside diameter smaller than thatof the glass portion of a general optical fiber, and the coatingthickness can be formed to be smaller than the coating thickness of ageneral optical fiber. Therefore, the outside diameter of the opticalfiber 10 can be smaller than the outside diameter of a general opticalfiber, and the diameter of the optical fiber 10 can be reduced. Byreducing the diameter of the optical fiber 10 in this way, the size ofthe tape core wire 4 can be smaller than the size of a general tape corewire. Therefore, the tape core wires 4 having such a small size areaccommodated in the slots 5S, and the number of cores of optical fiberaccommodated in the optical fiber cable 1 can be further increased.Alternatively, the tape core wires 4 having such a small size areaccommodated in the slots 5S, and the size of the optical fiber cable 1can be reduced.

On the other hand, as the accommodation density of the tape core wiresin the slots increases, the lateral pressure acting on the optical fibertends to increase. When the optical fiber receives the lateral pressurein this way, the shaft of the optical fiber is slightly bent, and themicrobend loss can occur. Furthermore, when the outside diameter of theglass portion of the optical fiber or the coating thickness of theoptical fiber is reduced, the glass portion is susceptible to thelateral pressure, and eventually the microbend loss can occur.

However, the optical fiber 10 of the present embodiment is formed sothat the value of the microbend loss characteristic factor F_(μBL_GO)described later is 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10²⁷) or less.Therefore, even when the outside diameter of the glass portion and thecoating thickness are reduced and the number of cores of the opticalfiber 10 accommodated in the slots 5S is increased, the microbend losscan be suppressed. The reason for this will be described in detailbelow.

The microbend loss of optical fiber is, as described in Non-PatentLiterature 1 (J. Baldauf, et al., “Relationship of MechanicalCharacteristics of Dual Coated Single Mode Optical Fibers andMicrobending Loss, “IEICE Trans. Commun., vol. E76-B, No. 4, 1993) andNon-Patent Literature 2 (C. Unger, et al., “Characterization of thebending sensitivity of fibers by the MAC-value, “Optics Communicationsvol. 107, no. 5-6, pp. 361-364, 1994), tends to be affected by both thegeometry and the optical characteristics of the optical fiber.

Here, the geometry of the optical fiber is a parameter related to thestructure of the optical fiber, and is, in the present embodiment, thespring coefficient κs of the primary coating layer of the optical fiber,the bending rigidity H_(f) of the glass portion, the deformationresistance Do of the secondary coating layer, the bending rigidity H₀ ofthe secondary coating layer, the Young's modulus E_(g) of the glassportion, the Young's modulus E_(p) of the primary coating layer, theYoung's modulus E_(s) of the secondary coating layer, the outsidediameter d_(f) of the glass portion (diameter of the glass portion), theradius R_(p) of the primary coating layer, the radius R_(s) of thesecondary coating layer, the thickness t_(p) of the primary coatinglayer, and the thickness t_(s) of the secondary coating layer.

Furthermore, the optical characteristics of the optical fiber areparameters related to the characteristics of the light propagatingthrough the optical fiber, and are, in the present embodiment, the modefield diameter 2w of the light propagating through the optical fiber,the cutoff wavelength λ_(cc) of the optical fiber, and the macrobendloss (bending loss) α_(BL) of the optical fiber.

The microbend loss of such an optical fiber may be represented by thevalue of sandpaper tension winding loss increase, which is thedifference between the transmission loss measured in a state where theoptical fiber is wound in one layer with a predetermined tension on aroughened bobbin body portion and the transmission loss measured in astate where the optical fiber is unwound from the bobbin with almost notension applied. The smaller the value of such sandpaper tension windingloss increase becomes, the smaller is the microbend loss of the opticalfiber.

By the way, the tape slot type cable (RSCC) such as the optical fibercable 1 of the present embodiment can cause the microbend loss asdescribed above. Therefore, the tape slot type cable has the requiredcharacteristics that the value of sandpaper tension winding lossincrease is 0.6 dB/km or less in consideration of such microbend loss.

The relationship between the sandpaper tension winding loss increase andthe aforementioned various parameters regarding the optical fiber usedfor the optical fiber cable were studied. As a result, it was found thata value of microbend loss characteristic factor F_(μBL_GO) representedby the formula (3) belowF _(μBL_GO) =F _(μBL_G) ×F _(μBL_O)  (3)

-   -   by using    -   geometry microbend loss characteristic F_(μBL_G) determined by        the formula (1) below

$\begin{matrix}{\mspace{76mu}{{F_{\mu\;{BL}\;\_\; G} = \frac{K_{S}^{2}}{H_{f}^{2} \times D_{0}^{1.125 - {0.25\mu}} \times H_{0}^{0.25 - 0.125}}}{{K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {R_{s}^{4} - R_{p}^{4}} \right)}}}}}} & (1)\end{matrix}$

related to a spring coefficient κs of the primary coating layer, abending rigidity H_(f) of the glass portion, a deformation resistance Doof the secondary coating layer, a bending rigidity H₀ of the secondarycoating layer, a Young's modulus E_(g) of the glass portion, a Young'smodulus E_(p) of the primary coating layer, a Young's modulus E_(s) ofthe secondary coating layer, an outside diameter d_(f) of the glassportion, a radius R_(p) of the outer peripheral surface of the primarycoating layer, a radius R_(s) of the outer peripheral surface of thesecondary coating layer, a thickness t_(p) of the primary coating layer,and a thickness t_(s) of the secondary coating layer, which areparameters related to geometry,

and

optical microbend loss characteristic F_(μBL_O) determined by theformula (2) below

$\begin{matrix}{F_{\mu\;{BL}\;\_\; O} = {\frac{2w}{\lambda_{cc}} \times \alpha_{BL}}} & (2)\end{matrix}$

related to a mode field diameter 2w, a cutoff wavelength λ_(cc) of theoptical fiber, and a macrobend loss α_(BL), which are parameters relatedto optical characteristics, has a high correlation with the value ofsandpaper tension winding loss increase. That is, the value of themicrobend loss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase.

Note that according to Non-Patent Literature 3 (K. Kobayashi, et al.,“Study of Microbending loss in thin coated fibers and fiber ribbons,”IWCS, pp. 386-392, 1993), the typical value of the constant μ in theaforementioned formula (1) is “3”. Therefore, the aforementioned formula(1) becomes the formula (4) described below.

$\begin{matrix}{\mspace{20mu}{{F_{\mu\;{BL}\;\_\; G} = \frac{K_{S}^{2}}{H_{f}^{2} \times D_{0}^{0.375} \times H_{0}^{0.625}}}{{K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {R_{s}^{4} - R_{p}^{4}} \right)}}}}}} & (4)\end{matrix}$

Furthermore, when the value of the aforementioned microbend losscharacteristic factor is 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10²⁷), thevalue of the sandpaper tension winding loss increase is a value slightlysmaller than 0.6 dB/km. As described above, the value of the microbendloss characteristic factor has a substantially positive slopeproportional relationship with the value of sandpaper tension windingloss increase. Therefore, by setting the value of the microbend losscharacteristic factor of the optical fiber to 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10²⁷) or less, the microbend loss can besuppressed to the extent that the required characteristics of the tapeslot type cable are satisfied.

As described above, the optical fiber 10 of the present embodiment isformed so that the value of the microbend loss characteristic factorF_(μBL_GO) is 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less. Therefore,in the optical fiber of the present embodiment, the microbend loss canbe suppressed to the extent that the required characteristics of thetape slot type cable are satisfied. Therefore, the optical fiber cable 1using the optical fiber 10 can exhibit favorable opticalcharacteristics.

Furthermore, as described above, in the optical fiber 10 of the presentembodiment, even when the outside diameter d_(f) of the glass portion 13is made smaller than 125 μm or the coating thickness t is made smallerthan 60 μm, because parameters other than the outside diameter d_(f) ofthe glass portion and the coating thickness t are adjusted so that thevalue of the microbend loss characteristic factor F_(μBL_GO) is 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, the microbend loss can besuppressed to the extent that the required characteristics of the tapeslot type cable are satisfied. Here, as shown in FIG. 3, the outsidediameter 2R₅ of the optical fiber 10 is represented by2R _(s) =d _(f)+2tusing the outside diameter d_(f) of the glass portion and the coatingthickness t. Therefore, as described above, the diameter of the opticalfiber can be reduced by reducing the coating thickness t and the outsidediameter d_(f) of the glass portion. Therefore, by using the opticalfiber 10 whose diameter is reduced and microbend loss is suppressed inthis way, a tape slot type cable having excellent opticalcharacteristics that realizes an increase in the number of cores and asmall size can be configured.

Second Embodiment

Next, the second embodiment will be described with reference to FIG. 4.FIG. 4 is a diagram schematically showing a structure of a cross sectionperpendicular to a longitudinal direction of an optical fiber cable 2according to the present embodiment. Note that the same or equivalentcomponents as those of the first embodiment are designated by the samereference numerals and duplicated description will be omitted unlessotherwise specified.

As shown in FIG. 4, the optical fiber cable 2 of the present embodimenthas the same configuration as the optical fiber cable 1 of the firstembodiment in that tape core wires 4 having substantially the sameconfiguration as that of the first embodiment are accommodated inside.However, the optical fiber cable 2 is mainly different from the opticalfiber cable 1 on the points described below.

The optical fiber cable 1 is a tape slot type cable (RSCC) as describedabove. On the other hand, as shown in FIG. 4, the optical fiber cable 2of the present embodiment does not have the holding body 5. That is, theoptical fiber cable 2 is a so-called small-diameter high-density cable(UHDC: Ultra-High Density Cable) in which the tape core wires are notaccommodated in the slots of the holding body but are directlyaccommodated in the sheath. That is, an accommodation space 3S is formedinside the sheath 3 of the optical fiber cable 2, and a plurality oftape core wires 4 are arranged in the accommodation space 3S. Note thatthe tensile strength bodies 6 may be embedded in the sheath 3 of theoptical fiber cable 2 at positions facing each other across the centerof the optical fiber cable 2.

Furthermore, as described above, the tape core wire 4 of the presentembodiment has substantially the same configuration as the tape corewire 4 of the first embodiment. However, the value of the microbend losscharacteristic factor F_(μBL_GO) of the optical fiber 10 included in thetape core wire 4 of the present embodiment is 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less for the reason describedlater.

Since the small-diameter high-density cable such as the optical fibercable 2 does not have the holding body 5 as described above and isslotless, the tape core wires 4 can be densely arranged in theaccommodation space 3S of the sheath 3. Therefore, a large number oftape core wires can be accommodated as compared with the tape slot typecable such as the optical fiber cable 1.

On the other hand, in the small-diameter high-density cable, since manytape core wires are densely arranged in one place as described above, alarge lateral pressure tends to be applied to the optical fiber ascompared with the tape slot type cable. Therefore, in the small-diameterhigh-density cable, it is recommended to use an optical fiber having asmaller microbend loss than the optical fiber used for the tape slottype cable. In view of the above, the small-diameter high-density cablehas the required characteristics that the value of the aforementionedsandpaper tension winding loss increase is 0.34 dB/km or less.

The value of the microbend loss characteristic factor F_(μBL_GO)corresponding to the value (0.34 dB/km) of the sandpaper tension windingloss increase may be calculated on the basis of the aforementionedformulae (2) to (4) and the value may be 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷). That is, by setting the value of themicrobend loss characteristic factor F_(μBL_GO) to 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, the microbend loss can besuppressed to the extent that the required characteristics of thesmall-diameter high-density cable are satisfied.

As described above, the optical fiber 10 of the present embodiment isconfigured so that the aforementioned various parameters are adjusted sothat the value of the microbend loss characteristic factor F_(μBL_GO) is1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less. Therefore, the microbendloss can be suppressed to the extent that the required characteristicsof the small-diameter high-density cable are satisfied. Therefore, theoptical fiber cable 2 using the optical fiber 10 can exhibit favorableoptical characteristics.

Furthermore, as described above, in the optical fiber 10 of the presentembodiment, even when the optical fiber 10 has a reduced diameter bymaking the outside diameter d_(f) of the glass portion 13 smaller than125 μm and the coating thickness t smaller than 57.5 μm, the microbendloss can be suppressed to the extent that the required characteristicsof the small-diameter high-density cable are satisfied. Therefore, byusing the optical fiber 10 whose diameter is reduced in this way, asmall-diameter high-density cable having excellent opticalcharacteristics that realizes an increase in the number of cores and asmall size can be configured.

Next, the reason why the outside diameter d_(f) of the glass portion 13can be small, the reason why the coating thickness of the optical fiber10 can be small, the reason why the outside diameter of the opticalfiber 10 can be small, and the like will be described.

The following Examples 1 to 48 are performed in order to verify therelationship between the value of the microbend loss characteristicfactor F_(μBL_GO) and the value of the sandpaper tension winding lossincrease α_(μBL). Note that embodiments of the invention are not limitedto Examples 1 to 48.

Examples 1 to 22

Samples 1 to 22 of optical fiber were prepared in which theaforementioned various parameters were changed, measured the value ofsandpaper tension winding loss increase for each of Samples 1 to 22, andcalculated the value of the microbend loss characteristic factorF_(μBL_GO) on the basis of the aforementioned formulae (2) to (4). Theoptical fiber of Sample 1 is the optical fiber of Example 1, and theoptical fiber of Sample 2 is the optical fiber of Example 2. Thus, thesample numbers of the optical fibers correspond to the numbers of theExamples. Note that the optical fiber of Sample 8 is an optical fibergenerally used for an optical fiber cable constituting the communicationinfrastructures, and has an outside diameter of the glass portion of 125μm and a coating thickness of 57.5 μm. The optical fiber of Sample 8 maybe referred to as the “general optical fiber”.

The test for sandpaper tension winding loss increase was performed inthe manner described below. That is, first, sandpaper (SiC having anaverage particle diameter of 50 μm (for example, model number #360)) waswound around the bobbin body portion having a body diameter of 380 mm,and one layer of optical fiber wire was wound therearound at 100 gf, andlight having a wavelength of 1550 nm was caused to propagate. Thetransmission loss at this time was measured. Thereafter, the opticalfiber wire was unwound from the bobbin, light having a wavelength of1550 nm was caused to propagate with almost no tension applied, and thetransmission loss was measured. Then, the difference between thesetransmission losses was obtained, and the value of this difference wasdefined as sandpaper tension winding loss increase α_(μBL).

Tables 1 to 5 below show the parameter specifications for each ofSamples 1 to 22, the values of the microbend loss characteristic factorF_(μBL_GO) for each of Samples 1 to 22, and the values of sandpapertension winding loss increase α_(μBL) for each of Samples 1 to 22.

Note that in Tables 1 to 5 below and Tables 7 to 10 described below,mode field diameter (MFD), cutoff wavelength, macrobend loss, and thelike are as described below. The mode field diameter is the mode fielddiameter of light in the LP01 mode when light having a wavelength of1310 nm is caused to propagate through the optical fiber.

Note that the aforementioned mode field diameter is expressed byPetermann II definition formula (formula (5) below) in ITU-TRecommendation G.650.1. Here, E(r) represents the electric fieldstrength at the point where the distance from the central axis of theoptical fiber is r.

$\begin{matrix}{{MFD} = {{2w} = {2\sqrt{\frac{2{\underset{0}{\int\limits^{\infty}}{{E^{2}(r)}{rdr}}}}{\underset{0}{\int\limits^{\infty}}{\left\lbrack {{{dE}(r)}/{dr}} \right\rbrack^{2}{rdr}}}}}}} & (5)\end{matrix}$

Furthermore, the aforementioned cutoff wavelength indicates the minimumwavelength at which the high-order mode is sufficiently attenuated. Thishigh-order mode refers to, for example, LP11 mode. Specifically, it isthe minimum wavelength at which the loss of the high-order mode is 19.3dB. The cutoff wavelength includes a fiber cutoff wavelength and a cablecutoff wavelength, and can be measured by, for example, the measurementmethod described in ITU-T Recommendation G.650. The cutoff wavelengthsdescribed in Tables 1 to 5 are cable cutoff wavelengths. Furthermore,the MAC value is the ratio of the mode field diameter 2w at a wavelengthof 1310 nm to the cable cutoff wavelength λ_(cc) and is defined as2w/λ_(cc). Furthermore, the macrobend losses shown in Tables 1 to 5 arethe bend loss of light caused by light having a wavelength of 1625 nmpropagating through a bent portion formed when the optical fiber is bentwith a radius of 10 mm. The unit “/turn” of macrobend loss means “perturn of optical fiber”. Furthermore, the propagation constant differenceis the difference between the propagation constant of light having awavelength of 1550 nm in the waveguide mode and the propagation constantof light having a wavelength of 1550 in the radiation mode, and, in thisexperiment, is the difference between the propagation constant of lighthaving a wavelength of 1550 nm in the LP01 mode and the propagationconstant in the LP11 mode. The propagation constant was calculated usingthe two-dimensional finite element method described in Non-PatentLiterature 4 (K. Saitoh and M. Koshiba, “Full-VectorialImaginary-Distance Beam Propagation Method Based on a Finite ElementScheme: Application to Photonic Crystal Fibers,” IEEE J. Quant. Elect.vol. 38, pp. 927-933, 2002) on the basis of the refractive index profileof a prototyped optical fiber. The zero dispersion wavelength refers toa wavelength at which the value of the wavelength dispersion becomeszero. Here, the wavelength dispersion is the sum of material dispersionand waveguide dispersion. Furthermore, the zero dispersion slope refersto the rate of change of wavelength dispersion with respect to thewavelength at the zero dispersion wavelength.

TABLE 1 Example 1 2 3 4 5 Outside diameter of 80 80 80 125 80 glassportion(μm) Outside diameter of 125 115 115 159 115 primary coatinglayer(μm) Outside diameter of 156 152 164 193 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.5 0.2 primary coating layer(MPa) Young'smodulus of 1150 1400 1400 1150 1400 secondary coating layer(MPa)Thickness of primary 22.5 17.5 17.5 17 17.5 coating layer(μm) Thicknessof secondary 15.5 18.5 24.5 17 19 coating layer(μm) Coatingthickness(μm) 38 36 42 34 36.5 Bending rigidity of 1.49 × 10¹¹ 1.49 ×10¹¹ 1.49 × 10¹¹ 8.87 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴)Bending rigidity of 1.97 × 10¹⁰ 2.47 × 10¹⁰ 3.77 × 10¹⁰ 4.22 × 10¹⁰ 2.56× 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa)0.71 0.91 0.91 3.68 0.91 Deformation resistance of 9.22 20.39 37.54 6.7921.65 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ · μm^(−10.5)· 3.66 3.90 2.38 1.92 3.72 10⁻²⁷) Mode field diameter(μm) 8.83 8.66 8.668.6 8.6 Cable cutoff wavelength(μm) 1.230 1.230 1.230 1.230 1.200 MACvalue(a.u.) 7.18 7.04 7.04 6.99 7.17 Macrobend loss(dB/turn) 0.100 0.0500.050 0.050 0.200 Propagation constant 12498 13182 13182 13066 11613difference (rad/m) Zero dispersion 1.311 1.316 1.316 1.317 1.310wavelength(μm) Zero dispersion 0.088 0.086 0.086 0.086 0.087slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 0.72 0.35 0.35 0.35 1.43F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) · 2.63 1.37 0.84 0.67 5.33dB/turn} · 10⁻²⁷) Sandpaper tension winding 0.85 0.46 0.3 0.22 0.98 lossincrease(dB/km)

TABLE 2 Example 6 7 8 9 10 Outside diameter of 80 125 125 80 80 glassportion(μm) Outside diameter of 115 159 190 113 113 primary coatinglayer(μm) Outside diameter of 153 193 240 164 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 114 74 glass portion(GPa) Young'smodulus of 0.2 0.5 0.6 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 800 1150 1150 secondary coating layer(MPa)Thickness of primary 17.5 17 32.5 16.5 16.5 coating layer(μm) Thicknessof secondary 19 17 25 25.5 20 coating layer(μm) Coating thickness(μm)36.5 34 57.5 42 36.5 Bending rigidity of 1.49 × 10¹¹ 8.87 × 10¹¹ 8.87 ×10¹¹ 2.29 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidityof 2.11 × 10¹⁰ 4.22 × 10¹⁰ 7.91 × 10¹⁰ 3.16 × 10¹⁰ 2.17 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa) 0.91 3.68 2.310.97 0.97 Deformation resistance of 17.82 6.79 7.83 34.78 20.75secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) · 4.531.92 0.48 1.29 4.72 10⁻²⁷) Mode field diameter(μm) 8.48 8.5 8.55 8.518.47 Cable cutoff wavelength(μm) 1.209 1.203 1.197 1.287 1.330 MACvalue(a.u.) 7.01 7.07 7.14 6.61 6.37 Macrobend loss(dB/turn) 0.200 0.0910.133 0.013 0.035 Propagation constant 11403 11971 11623 14259 14296difference (rad/m) Zero dispersion 1.313 1.313 1.313 1.309 1.309wavelength(μm) Zero dispersion 0.085 0.086 0.086 0.091 0.091slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 1.40 0.65 0.95 0.09 0.22F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) · 6.35 1.24 0.47 0.11 1.05dB/turn} · 10⁻²⁷) Sandpaper tension winding 1.5 0.3 0.05 0.218 0.315loss increase(dB/km)

TABLE 3 Example 11 12 13 14 15 Outside diameter of 80 80 80 80 90 glassportion (μm) Outside diameter of 114 114 115 115 121 primary coatinglayer(μm) Outside diameter of 153 164 153 153 159 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 1150 1400 1150 secondary coating layer(MPa)Thickness of primary 17 17 17.5 17.5 15.5 coating layer(μm) Thickness ofsecondary 19.5 25 19 19 19 coating layer(μm) Coating thickness(μm) 36.542 36.5 36.5 34.5 Bending rigidity of 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 ×10¹¹ 1.49 × 10¹¹ 2.38 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidityof 2.14 × 10¹⁰ 3.13 × 10¹⁰ 2.11 × 10¹⁰ 2.56 × 10¹⁰ 2.40 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa) 0.94 0.94 0.910.91 1.16 Deformation resistance of 19.25 32.79 17.82 21.65 15.90secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) · 4.612.98 4.53 3.72 2.74 10⁻²⁷) Mode field diameter(μm) 8.47 8.5 8.36 8.48.52 Cable cutoff wavelength(μm) 1.357 1.367 1.174 1.188 1.221 MACvalue(a.u.) 6.24 6.22 7.12 7.07 6.98 Macrobend loss(dB/turn) 0.010 0.0100.080 0.040 0.040 Propagation constant 15223 15007 13198 15278 14687difference (rad/m) Zero dispersion 1.309 1.309 1.310 1.310 1.309wavelength(μm) Zero dispersion 0.091 0.091 0.089 0.089 0.091slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 0.06 0.06 0.57 0.28 0.28F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) · 0.29 0.19 2.58 1.05 0.76dB/turn} · 10⁻²⁷) Sandpaper tension winding 0.231 0.289 0.57 0.27 0.197loss increase(dB/km)

TABLE 4 Example 16 17 18 19 20 Outside diameter of 90 90 80 80 80 glassportion (μm) Outside diameter of 121 121 115 115 115 primary coatinglayer(μm) Outside diameter of 159 159 153 164 153 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young'smodulus of 1150 1150 1150 1150 1150 secondary coating layer(MPa)Thickness of primary 15.5 15.5 17.5 17.5 17.5 coating layer(μm)Thickness of secondary 19 19 19 24.5 19 coating layer(μm) Coatingthickness(μm) 34.5 34.5 36.5 42 36.5 Bending rigidity of 2.38 × 10¹¹2.38 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴)Bending rigidity of 2.40 × 10¹⁰ 2.40 × 10¹⁰ 2.11 × 10¹⁰ 3.10 × 10¹⁰ 2.11× 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 κ_(s)(MPa)1.16 1.16 0.91 0.91 0.91 Deformation resistance of 15.90 15.90 17.8230.87 17.82 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 2.74 2.74 4.53 2.90 4.53 10⁻²⁷) Mode field diameter(μm)8.506 8.46 7.645 7.64 7.607 Cable cutoff wavelength(μm) 1.270 1.2861.184 1.245 1.271 MAC value(a.u.) 6.70 6.58 6.46 6.14 5.99 Macrobendloss(dB/turn) 0.017 0.008 0.070 0.006 0.004 Propagation constant 1439215187 12929 13865 14825 difference (rad/m) Zero dispersion 1.309 1.3091.336 1.336 1.336 wavelength(μm) Zero dispersion 0.091 0.091 0.079 0.0790.079 slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 0.11 0.05 0.45 0.040.02 F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) · 0.31 0.14 2.05 0.11 0.11dB/turn} · 10⁻²⁷) Sandpaper tension winding 0.23 0.164 0.577 0.23 0.259loss increase(dB/km)

TABLE 5 Example 21 22 Outside diameter of 80 80 glass portion (μm)Outside diameter of 115 115 primary coating layer(μm) Outside diameterof 153 153 secondary coating layer(μm) Young's modulus of 74 74 glassportion(GPa) Young's modulus of 0.2 0.2 primary coating layer(MPa)Young's modulus of 1150 1400 secondary coating layer(MPa) Thickness ofprimary 17.5 17.5 coating layer(μm) Thickness of secondary 19 19 coatinglayer(μm) Coating thickness(μm) 36.5 36.5 Bending rigidity of 1.49 ×10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of 2.11 ×10¹⁰ 2.56 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3κ_(s)(MPa) 0.91 0.91 Deformation resistance of 17.82 21.65 secondarycoating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ · μm^(−10.5) · 4.53 3.7210⁻²⁷) Mode field diameter(μm) 7.627 7.7 Cable cutoff wavelength(μm)1.300 1.183 MAC value(a.u.) 5.87 6.51 Macrobend loss(dB/turn) 0.0010.040 Propagation constant 15702 13192 difference (rad/m) Zerodispersion 1.336 1.339 wavelength(μm) Zero dispersion 0.079 0.079slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 0.01 0.26 F_(μBL) _(—) _(GO)({GPa⁻¹ · μm^(−10.5) · 0.03 0.97 dB/turn} · 10⁻²⁷) Sandpaper tensionwinding 0.165 0.334 loss increase(dB/km)

The values of the microbend loss characteristic factor F_(μBL_GO) andthe values of the sandpaper tension winding loss increase α_(μBL) ofeach of Samples 1 to 22 were plotted with respect to a coordinate systemin which the value of microbend loss characteristic factor F_(μBL_GO) ison the horizontal axis (X-axis) and the value of sandpaper tensionwinding loss increase α_(μBL) is on the vertical axis (Y-axis). As aresult, the scatter diagram shown in FIG. 5 was obtained. When thefunction was obtained from this scatter diagram using the least-squaresmethod, a linear function with a positive slope represented by theformula (6) below was obtained. Furthermore, the correlation coefficientof the data in FIG. 5 was 89% or more.Y=0.2355X  (6)

That is, it was found that the value of the microbend losscharacteristic factor F_(μBL_GO) and the value of the sandpaper tensionwinding loss increase α_(μBL) had a high correlation, and specificallythe value of the microbend loss characteristic factor F_(μBL_GO) and thevalue of the sandpaper tension winding loss increase α_(μBL) had aproportional relationship having a generally positive slope.

By the way, as described above, the tape slot type cable (RSCC) has therequired characteristics that the value of the sandpaper tension windingloss increase α_(μBL) is 0.60 (dm/km) or less. Furthermore, thesmall-diameter high-density cable (UHDC) has the requiredcharacteristics that the value of the sandpaper tension winding lossincrease α_(μBL) is 0.34 (dm/km) or less. Therefore, Table 6 belowindicates the values of the microbend loss characteristic factorF_(μBL_GO), the values of the sandpaper tension winding loss increaseα_(μBL), the pass/fail of the required characteristics of the tape slottype cable (RSCC), and the pass/fail of the required characteristics ofthe small-diameter high-density cable (UHDC) of Examples 1 to 22. Notethat in Table 6, Y means that the required characteristics aresatisfied, and N means that the required characteristics are notsatisfied.

TABLE 6 F_(μBL) _(—) _(GO) ({GPa⁻¹ · α μBL μm^(−10.5) · dB/ Applicationto RSCC Application to UHDC Example (dB/km) turn} · 10⁻²⁷) (F_(μBL) _(—)_(GO) ≤ 2.6) (F_(μBL) _(—) _(GO) ≤ 1.3) 21 0.17 0.03 Y Y 19 0.23 0.11 YY 20 0.26 0.11 Y Y 9 0.22 0.11 Y Y 17 0.16 0.14 Y Y 12 0.29 0.19 Y Y 110.23 0.29 Y Y 16 0.23 0.31 Y Y 8 0.05 0.46 Y Y 4 0.22 0.67 Y Y 15 0.200.76 Y Y 3 0.30 0.84 Y Y 22 0.33 0.97 Y Y 10 0.32 1.05 Y Y 14 0.27 1.05Y Y 7 0.30 1.24 Y Y 2 0.46 1.37 Y N 18 0.58 2.05 Y N 13 0.57 2.58 Y N 10.85 2.63 N N 5 0.98 5.33 N N 6 1.50 6.35 N N

From Table 6, it was found that when the value of the microbend losscharacteristic factor F_(μBL_GO) is 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, the value of the sandpapertension winding loss increase α_(μBL) tends to be approximately 0.60 orless and when the value of the microbend loss characteristic factorF_(μBL_GO) is larger than 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷), thevalue of the sandpaper tension winding loss increase α_(μBL) tends toexceed 0.60. In other words, it was found that the requiredcharacteristics of the tape slot type cable can be satisfied byadjusting the values of the parameters described in Tables 1 to 5described above so that the value of the microbend loss characteristicfactor F_(μBL_GO) is 2.6 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less.

Furthermore, it was found that when the value of the microbend losscharacteristic factor F_(μBL_GO) is 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, the value of the sandpapertension winding loss increase α_(μBL) tends to be approximately 0.34 orless and when the value of the microbend loss characteristic factorF_(μBL_GO) is larger than 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷), thevalue of the sandpaper tension winding loss increase α_(μBL) tends toexceed 0.34. In other words, it was found that in addition to therequired characteristics of the tape slot type cable, the requiredcharacteristics of the small-diameter high-density cable can besatisfied by adjusting the values of the parameters described in Tables1 to 5 described above so that the value of the microbend losscharacteristic factor F_(μBL_GO) is 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less.

Specifically, among Samples 1 to 22, the samples satisfying the requiredcharacteristics of the tape slot type cable were the samples excludingSamples 1, 5, and 6. Furthermore, the samples satisfying the requiredcharacteristics of the small-diameter high-density cable in addition tothe required characteristics of the tape slot type cable were thesamples excluding Examples 1, 2, 5, 6, 13, and 18.

Furthermore, among the samples satisfying at least the requiredcharacteristics of the tape slot type cable among Samples 1 to 22, itwas found that the samples excluding Samples 4, 7, and 8 have an outsidediameter of the glass portion of 80 μm or 90 μm smaller than the outsidediameter (125 μm) of the glass portion of the general optical fiber.Specifically, it was found that Samples 2, 3, 9 to 14, and 18 to 22 havean outside diameter of the glass portion of 80 μm, and Samples 15 to 17have an outside diameter of the glass portion of 90 μm. That is, it wasfound that, by adjusting the parameters as in Samples 2, 3, and 9 to 22,an optical fiber that satisfies at least the required characteristics ofthe tape slot type cable and has the outside diameter of the glassportion smaller than that of the general optical fiber can be formed.

Furthermore, it was found that the samples, excluding Sample 8,satisfying at least the required characteristics of the tape slot typecable among Samples 1 to 22 have a coating thickness smaller than thecoating thickness (approximately 57.5 μm) of the general optical fiber.Specifically, it was found that Samples 3, 9, and 12 have a coatingthickness of 42.0 μm, Samples 10, 11, 13, 14, 18, and 20 to 22 have acoating thickness of 36.5 μm, Sample 2 has a coating thickness of 36.0μm, Samples 15 to 17 have a coating thickness of 34.5 μm, and Samples 4and 7 have a coating thickness of 34.0 μm. That is, it was found that,by adjusting the parameters as in Samples 2 to 4, 7, and 9 to 22, anoptical fiber that satisfies at least the required characteristics ofthe tape slot type cable and has the coating thickness smaller than thatof the general optical fiber can be formed.

As described above, it was found that, among Samples 1 to 22, thesamples excluding Samples 1, 5, 6, and 8 satisfy at least the requiredcharacteristics of the tape slot type cable and have the outsidediameter of the glass portion and the coating thickness smaller thanthose of the general optical fiber. By forming both the outside diameterof the glass portion and the coating thickness to be smaller than theoutside diameter of the glass portion and the coating thickness of thegeneral optical fiber, it is possible to effectively realize a reductionin diameter of the optical fiber.

Furthermore, the optical fibers of Samples 1 to 22 have an MFD of 7.6 μmor more. When the MFD is too small, an MFD mismatch can occur whenconnection to a general-purpose optical fiber is established. However,when the MFD of the optical fiber is 7.6 μm or more, the MFD mismatchwhen connection to a general-purpose optical fiber is established can besmall. Therefore, the occurrence of connection loss can be effectivelysuppressed.

Moreover, the optical fibers of Samples 5 to 8 meet the internationalstandard ITU-.G.657.A1. That is, the MFD at a wavelength of 1310 nm is8.2 μm or more and 9.6 μm or less, the cable cutoff wavelength is 1260nm or less, the zero dispersion wavelength is 1300 to 1324 nm, the zerodispersion slope is 0.073 ps/km/nm or more and 0.092 ps/km/nm or less,and the macrobend loss at a wavelength of 1625 nm by bending at a radiusof 10 mm is 1.5 dB/turn or less. Furthermore, the optical fibers ofSamples 1 to 4 satisfy ITU-T.G.657.A2. That is, the MFD at a wavelengthof 1310 nm is 8.2 μm or more and 9.6 μm or less, the cable cutoffwavelength is 1260 nm or less, the zero dispersion wavelength is 1300 nmor more and 1324 nm or less, the zero dispersion slope is 0.073 ps/km/nmor more and 0.092 ps/km/nm or less, and the macrobend loss at awavelength of 1625 nm by bending at a radius of 10 mm is 0.2 dB/turn orless. Furthermore, the optical fibers of Samples 13 to 15 satisfyITU-T.G.657.B3. That is, the MFD at a wavelength of 1310 nm is 8.2 μm ormore and 9.6 μm or less, the cable cutoff wavelength is 1260 nm or less,the zero dispersion wavelength is 1300 nm or more and 1324 nm or less,the zero dispersion slope is 0.073 ps/km/nm or more and 0.092 ps/km/nmor less, and the macrobend loss at a wavelength of 1625 nm by bending ata radius of 10 mm is 0.1 dB/turn or less.

Examples 23 to 28

Furthermore, the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 23 to 28 of optical fiber were determined andadjusted as indicated in Table 7 below on the assumption of an opticalfiber having the same optical characteristics as Samples 16, 17, and 19,specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss (bending loss), propagation constant difference, zerodispersion wavelength, and zero dispersion slope as those samples, thesame thickness of the primary coating layer and thickness of thesecondary coating layer as those of Sample 19, and an outside diameterof the glass portion of 65 μm.

TABLE 7 Example 23 24 25 26 27 28 Outside diameter of 65 65 65 65 65 65glass portion (μm) Outside diameter of 100 100 100 100 100 100 primarycoating layer(μm) Outside diameter of 149 149 149 149 149 149 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.2 0.2 0.2 0.2 0.2 0.2 primary coatinglayer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150 secondarycoating layer(MPa) Thickness of primary 17.5 17.5 17.5 17.5 17.5 17.5coating layer(μm) Thickness of secondary 24.5 24.5 24.5 24.5 24.5 24.5coating layer(μm) Coating thickness(μm) 42 42 42 42 42 42 Bendingrigidity of 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰ 6.48 × 10¹⁰6.48 × 10¹⁰ glass portion(MPa · μm⁴) Bending rigidity of 2.70 × 10¹⁰2.22 × 10¹⁰ 2.70 × 10¹⁰ 2.22 × 10¹⁰ 2.70 × 10¹⁰ 2.22 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 0.74 0.74 0.740.74 0.74 0.74 Deformation resistance of 49.99 41.10 49.99 41.10 49.9941.10 secondary coating layer(MPa) F_(μ BL) _(—) _(G)(GPa⁻¹ · μm^(−10.5)· 9.15 11.14 9.15 11.14 9.15 11.14 10⁻²⁷) Mode field diameter(μm) 7.647.64 8.506 8.506 8.46 8.46 Cable cutoff wavelength(μm) 1.245 1.245 1.2701.270 1.286 1.286 MAC value(a.u.) 6.14 6.14 6.70 6.70 6.58 6.58Macrobend loss(dB/turn) 0.006 0.006 0.017 0.017 0.008 0.008 Propagationconstant 13865 13865 14392 14392 15187 15187 difference (rad/m) Zerodispersion 1.336 1.336 1.309 1.309 1.309 1.309 wavelength(μm) Zerodispersion 0.079 0.079 0.091 0.091 0.091 0.091 slope(ps/km/nm²) F_(μBL)_(—) _(O)(dB/turn) 0.04 0.04 0.11 0.11 0.05 0.05 F_(μBL) _(—) _(GO)({GPa⁻¹ · μm^(−10.5) · 0.34 0.41 1.04 1.27 0.48 0.59 dB/turn} · 10⁻²⁷)Application to RSCC Y Y Y Y Y Y Application to UHDC Y Y Y Y Y Y

As indicated in Table 7, each of Samples 23 to 28 has an outsidediameter of the glass portion of 65 μm and a coating thickness of 42 μm.Furthermore, it was found that the values of the microbend losscharacteristic factor F_(μBL_GO) of Samples 23 to 28 are all 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, and Samples 23 to 28 satisfythe required characteristics of the tape slot type cable. Furthermore,it was found that the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 23 to 28 are all 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10 ⁻²⁷) or less, and Samples 23 to 28satisfy the required characteristics of the small-diameter high-densitycable in addition to the required characteristics of the tape slot typecable.

Examples 29 to 36

Furthermore, the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 29 to 36 of optical fiber were determined andadjusted as indicated in Tables 8 and 9 below on the assumption of anoptical fiber having the same optical characteristics as Samples 15, 16,17, and 19, specifically, the same MFD, cable cutoff wavelength, MACvalue, macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, the samethickness of the primary coating layer and thickness of the secondarycoating layer as those of Example 19, and an outside diameter of theglass portion of 70 μm.

TABLE 8 Example 29 30 31 32 Outside diameter of 70 70 70 70 glassportion (μm) Outside diameter of 105 105 105 105 primary coatinglayer(μm) Outside diameter of 154 154 154 154 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.15 0.15 primary coating layer(MPa) Young's modulusof 1400 1150 1400 1150 secondary coating layer(MPa) Thickness of primary17.5 17.5 17.5 17.5 coating layer(μm) Thickness of secondary 24.5 24.524.5 24.5 coating layer(μm) Coating thickness(μm) 42 42 42 42 Bendingrigidity of 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ glassportion(MPa · μm⁴) Bending rigidity of 3.03 × 10¹⁰ 2.49 × 10¹⁰ 3.03 ×10¹⁰ 2.49 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3κ_(s)(MPa) 0.80 0.80 0.60 0.60 Deformation resistance of 45.30 37.2445.25 37.19 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 5.66 6.89 3.19 3.88 10⁻²⁷) Mode field diameter(μm) 7.647.64 8.52 8.52 Cable cutoff wavelength(μm) 1.245 1.245 1.221 1.221 MACvalue(a.u.) 6.14 6.14 6.98 6.98 Macrobend loss(dB/turn) 0.006 0.0060.040 0.040 Propagation constant 13865 13865 14687 14687 difference(rad/m) Zero dispersion 1.336 1.336 1.309 1.309 wavelength(μm) Zerodispersion 0.079 0.079 0.091 0.091 slope(ps/km/nm²) F_(μBL) _(—)_(O)(dB/turn) 0.04 0.04 0.28 0.28 F_(μBL) _(—) _(GO) ({GPa⁻¹ ·μm^(−10.5) · 0.21 0.25 0.89 1.08 dB/turn} · 10⁻²⁷) Application to RSCC YY Y Y Application to UHDC Y Y Y Y

TABLE 9 Example 33 34 35 36 Outside diameter of 70 70 70 70 glassportion (μm) Outside diameter of 105 105 105 105 primary coatinglayer(μm) Outside diameter of 154 154 154 154 secondary coatinglayer(μm) Young's modulus of 74 74 74 74 glass portion(GPa) Young'smodulus of 0.2 0.2 0.2 0.2 primary coating layer(MPa) Young's modulus of1400 1150 1400 1150 secondary coating layer(MPa) Thickness of primary17.5 17.5 17.5 17.5 coating layer(μm) Thickness of secondary 24.5 24.524.5 24.5 coating layer(μm) Coating thickness(μm) 42 42 42 42 Bendingrigidity of 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ 8.72 × 10¹⁰ glassportion(MPa · μm⁴) Bending rigidity of 3.03 × 10¹⁰ 2.49 × 10¹⁰ 3.03 ×10¹⁰ 2.49 × 10¹⁰ secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3κ_(s)(MPa) 0.80 0.80 0.80 0.80 Deformation resistance of 45.30 37.2445.30 37.24 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 5.66 6.89 5.66 6.89 10⁻²⁷) Mode field diameter(μm) 8.5068.506 8.46 8.46 Cable cutoff wavelength(μm) 1.270 1.270 1.286 1.286 MACvalue(a.u.) 6.70 6.70 6.58 6.58 Macrobend loss(dB/turn) 0.017 0.0170.008 0.008 Propagation constant 14392 14392 15187 15187 difference(rad/m) Zero dispersion 1.309 1.309 1.309 1.309 wavelength(μm) Zerodispersion 0.091 0.091 0.091 0.091 slope(ps/km/nm²) F_(μBL) _(—)_(O)(dB/turn) 0.11 0.11 0.05 0.05 F_(μBL) _(—) _(GO) ({GPa⁻¹ ·μm^(−10.5) · 0.64 0.78 0.30 0.36 dB/turn} · 10⁻²⁷) Application to RSCC YY Y Y Application to UHDC Y Y Y Y

As indicated in Tables 8 and 9, each of Samples 29 to 36 has an outsidediameter of the glass portion of 70 μm and a coating thickness of 42 μm.Furthermore, it was found that the values of the microbend losscharacteristic factor F_(μBL_GO) of Samples 29 to 36 are all 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, and Samples 29 to 36 satisfythe required characteristics of the tape slot type cable. Furthermore,it was found that the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 29 to 36 are all 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, and Samples 29 to satisfythe required characteristics of the small-diameter high-density cable inaddition to the required characteristics of the tape slot type cable.

Examples 37 to 42

Furthermore, the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 37 to 42 of optical fiber were determined andadjusted as indicated in Table 10 below on the assumption of an opticalfiber having the same optical characteristics as Samples 15, 17, and 19,specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, the samethickness of the primary coating layer and thickness of the secondarycoating layer as those of Example 19, and an outside diameter of theglass portion of 75 μm.

TABLE 10 Example 37 38 39 40 41 42 Outside diameter of 75 75 75 75 75 75glass portion (μm) Outside diameter of 110 110 110 110 110 110 primarycoating layer(μm) Outside diameter of 159 159 159 159 159 159 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.2 0.2 0.2 0.2 0.2 0.2 primary coatinglayer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150 secondarycoating layer(MPa) Thickness of primary 17.5 17.5 17.5 17.5 17.5 17.5coating layer(μm) Thickness of secondary 24.5 24.5 24.5 24.5 24.5 24.5coating layer(μm) Coating thickness(μm) 42 42 42 42 42 42 Bendingrigidity of 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15 × 10¹¹ 1.15 × 10¹¹1.15 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of 3.39 × 10¹⁰2.78 × 10¹⁰ 3.39 × 10¹⁰ 2.78 × 10¹⁰ 3.39 × 10¹⁰ 2.78 × 10¹⁰ secondarycoating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 0.86 0.86 0.860.86 0.86 0.86 Deformation resistance of 41.18 33.86 41.18 33.86 41.1833.86 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ · μm^(−10.5)· 3.62 4.40 3.62 4.40 3.62 4.40 10⁻²⁷) Mode field diameter(μm) 7.64 7.648.52 8.52 8.46 8.46 Cable cutoff wavelength(μm) 1.245 1.245 1.221 1.2211.286 1.286 MAC value(a.u.) 6.14 6.14 6.98 6.98 6.58 6.58 Macrobendloss(dB/turn) 0.006 0.006 0.040 0.040 0.008 0.008 Propagation constant13865 13865 14687 14687 15187 15187 difference (rad/m) Zero dispersion1.336 1.336 1.309 1.309 1.309 1.309 wavelength(μm) Zero dispersion 0.0790.079 0.091 0.091 0.091 0.091 slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/tum)0.04 0.04 0.28 0.28 0.05 0.05 F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) ·0.13 0.16 1.01 1.23 0.19 0.23 dB/turn} · 10⁻²⁷) Application to RSCC Y YY Y Y Y Application to UHDC Y Y Y Y Y Y

As indicated in Table 10, each of Samples 37 to 42 has an outsidediameter of the glass portion of 75 μm and a coating thickness of 42 μm.Furthermore, it was found that the values of the microbend losscharacteristic factor F_(μBL_GO) of Samples 37 to 42 are all 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10 ⁻²⁷) or less, and Samples 37 to 42satisfy the required characteristics of the tape slot type cable.Furthermore, it was found that the values of the microbend losscharacteristic factor F_(μBL_GO) of Samples 37 to 42 are all 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, and Samples 37 to 42 satisfythe required characteristics of the small-diameter high-density cable inaddition to the required characteristics of the tape slot type cable.

Examples 43 to 48

Furthermore, the values of the microbend loss characteristic factorF_(μBL_GO) of Samples 43 to 48 of optical fiber were determined andadjusted as indicated in Table 11 below on the assumption of an opticalfiber having the same optical characteristics as Samples 15, 17, and 19,specifically, the same MFD, cable cutoff wavelength, MAC value,macrobend loss, propagation constant difference, zero dispersionwavelength, and zero dispersion slope as those samples, an outsidediameter of the secondary coating layer of 125 μm, and an outsidediameter of the glass portion of 80 μm.

TABLE 11 Example 43 44 45 46 47 48 Outside diameter of 80 80 80 80 80 80glass portion (μm) Outside diameter of 100 100 100 100 100 100 primarycoating layer(μm) Outside diameter of 125 125 125 125 125 125 secondarycoating layer(μm) Young's modulus of 74 74 74 74 74 74 glassportion(GPa) Young's modulus of 0.15 0.15 0.15 0.15 0.15 0.15 primarycoating layer(MPa) Young's modulus of 1400 1150 1400 1150 1400 1150secondary coating layer(MPa) Thickness of primary 10 10 10 10 10 10coating layer(μm) Thickness of secondary 12.5 12.5 12.5 12.5 12.5 12.5coating layer(μm) Coating thickness(μm) 22.5 22.5 22.5 22.5 22.5 22.5Bending rigidity of 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49 × 10¹¹ 1.49× 10¹¹ 1.49 × 10¹¹ glass portion(MPa · μm⁴) Bending rigidity of  9.91 ×10⁹  8.14 × 10⁹  9.91 × 10⁹  8.14 × 10⁹  9.91 × 10⁹  8.14 × 10⁹secondary coating layer(MPa · μm⁴) μ (a.u.) 3 3 3 3 3 3 κ_(s)(MPa) 1.201.20 1.20 1.20 1.20 1.20 Deformation resistance of 11.35 9.35 11.35 9.3511.35 9.35 secondary coating layer(MPa) F_(μBL) _(—) _(G)(GPa⁻¹ ·μm^(−10.5) · 14.80 17.99 14.80 17.99 14.80 17.99 10⁻²⁷) Mode fielddiameter(μm) 7.64 7.64 8.52 8.52 8.46 8.46 Cable cutoff wavelength(μm)1.245 1.245 1.221 1.221 1.286 1.286 MAC value(a.u.) 6.14 6.14 6.98 6.986.58 6.58 Macrobend loss(dB/turn) 0.006 0.006 0.040 0.040 0.008 0.008Propagation constant 13865 13865 14687 14687 15187 15187difference(rad/m) Zero dispersion 1.336 1.336 1.309 1.309 1.309 1.309wavelength(μm) Zero dispersion 0.079 0.079 0.091 0.091 0.091 0.091slope(ps/km/nm²) F_(μBL) _(—) _(O)(dB/turn) 0.04 0.04 0.28 0.28 0.050.05 F_(μBL) _(—) _(GO) ({GPa⁻¹ · μm^(−10.5) · 0.54 0.66 4.13 5.02 0.780.95 dB/turn} · 10⁻²⁷) Application to RSCC Y Y N N Y Y Application toUHDC Y Y N N Y Y

As indicated in Table 11, each of Samples 43 to 48 has an outsidediameter of the glass portion of 80 μm, an outside diameter of thesecondary coating layer of 125 μm, and a thickness of the coating layerof 22.5 μm. Furthermore, it was found that the values of the microbendloss characteristic factor F_(μBL_GO) of Samples 43, 44, 47, and 48 areall 1.3 ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less, and Samples 43, 44,47, and 48 satisfy the required characteristics of the small-diameterhigh-density cable in addition to the required characteristics of thetape slot type cable. Note that similar to Samples 43, 44, 47 and 48,Samples 45 and 46 have an outside diameter of the glass portion of 80μm, an outside diameter of the secondary coating layer of 125 μm, and athickness of the coating layer of 22.5 μm, but the values of themicrobend loss characteristic factor F_(μBL_GO) exceed 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷), and do not satisfy the requiredcharacteristics of the tape slot type cable or the requiredcharacteristics of the small-diameter high-density cable.

Although the present invention has been described above by taking theaforementioned embodiments as an example, the present invention is notlimited thereto.

For example, in the first and second embodiments described above, theexample in which the secondary coating layer is the outermost layer ofthe optical fiber has been described. However, even when a colored layeris further provided as a third coating layer on the outer periphery ofthe secondary coating layer, the secondary coating layer and the coloredlayer can be applied to one or more embodiments of the invention as asecond coating layer, i.e., the secondary coating layer as long as theYoung's modulus of the colored layer is not significantly different fromthe Young's modulus of the secondary coating layer.

According to one or more embodiments of the invention, an optical fibercapable of suppressing microbend loss is provided, and can be used in afield such as a communication infrastructure.

The invention claimed is:
 1. An optical fiber comprising a glass portioncomprising a core and a clad surrounding the core; a primary coatinglayer covering the clad; and a secondary coating layer covering theprimary coating layer, wherein a value of microbend loss characteristicfactor F_(μBL_GO) ([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) is 2.6([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less when represented byF _(μBL_GO) =F _(μBL_G) ×F _(μBL_O), wherein geometry microbend losscharacteristic F_(μBL_G) (GPa⁻¹·μm^(−10.5)·10⁻²⁷) of the optical fiberis represented by$\mspace{20mu}{F_{\mu\;{BL}\;\_\; G} = \frac{K_{S}^{2}}{H_{f}^{2} \times D_{0}^{0.375} \times H_{0}^{0.625}}}$${K_{s} = \frac{E_{p}d_{f}}{t_{p}}},{H_{f} = {\frac{\pi}{4}{E_{g}\left( \frac{d_{f}}{2} \right)}^{4}}},{D_{0} = {E_{p} + {\left( \frac{t_{s}}{R_{s}} \right)^{3}E_{s}}}},{H_{0} = {\frac{\pi}{4}{E_{s}\left( {R_{s}^{4} - R_{p}^{4}} \right)}}},$where κs (MPa) is a spring coefficient of the primary coating layer,H_(f) (MPa·μm⁴) is a bending rigidity of the glass portion, D₀ (MPa) isa deformation resistance of the secondary coating layer, H₀ (MPa·μm⁴) isa bending rigidity of the secondary coating layer, E_(g) (GPa) is aYoung's modulus of the glass portion, E_(p) (MPa) is a Young's modulusof the primary coating layer, E_(s) (MPa) is a Young's modulus of thesecondary coating layer, d_(f) (μm) is an outside diameter of the glassportion, R_(p) (μm) is a radius of an outer peripheral surface of theprimary coating layer, R_(s) (μm) is a radius of an outer peripheralsurface of the secondary coating layer, t_(p) (μm) is a thickness of theprimary coating layer, and t_(s) (μm) is a thickness of the secondarycoating layer, and wherein optical microbend loss characteristicF_(μBL_O) (dB/turn) of the optical fiber is represented by${F_{\mu\;{BL}\;\_\; O} = {\frac{2w}{\lambda_{cc}} \times \alpha_{BL}}},$where 2w (μm) is a mode field diameter of light having a wavelength of1310 nm propagating through the optical fiber, λ_(cc) (μm) is a cablecutoff wavelength of the optical fiber, and α_(BL) (dB/turn) is amacrobend loss of the optical fiber at a wavelength of 1625 nm and aradius of 10 mm.
 2. The optical fiber according to claim 1, wherein thevalue of the microbend loss characteristic factor is 1.3([GPa⁻¹·μm^(−10.5)·dB/turn]·10⁻²⁷) or less.
 3. The optical fiberaccording to claim 1, wherein a coating thickness of a sum of thethickness of the primary coating layer and the thickness of thesecondary coating layer is 42.0 μm or less.
 4. The optical fiberaccording to claim 3, wherein the coating thickness is 38.0 μm or less.5. The optical fiber according to claim 3, wherein the coating thicknessis 36.5 μm or less.
 6. The optical fiber according to claim 3, whereinthe coating thickness is 34.5 μm or less.
 7. The optical fiber accordingto claim 3, wherein the coating thickness is 34.0 μm or less.
 8. Theoptical fiber according to claim 3, wherein the outside diameter of theglass portion is 65 μm or more and 100 μm or less.
 9. The optical fiberaccording to claim 8, wherein the outside diameter of the glass portionis 90 μm or less.
 10. The optical fiber according to claim 8, whereinthe outside diameter of the glass portion is 80 μm or less.
 11. Theoptical fiber according to claim 8, wherein the outside diameter of theglass portion is 75 μm or less.
 12. The optical fiber according to claim8, wherein the outside diameter of the glass portion is 70 μm or less.13. The optical fiber according to claim 3, wherein the mode fielddiameter of light having a wavelength of 1310 nm is 7.6 μm or more and8.7 μm or less, the cable cutoff wavelength is 1260 nm or less, zerodispersion wavelength is 1300 nm or more and 1324 nm or less, and zerodispersion slope is 0.073 ps/km/nm or more and 0.092 ps/km/nm or less.14. The optical fiber according to claim 13, wherein the macrobend lossof light having a wavelength of 1625 nm by bending at a radius of 10 mmis 1.5 dB/turn or less.
 15. The optical fiber according to claim 13,wherein the macrobend loss of light having a wavelength of 1625 nm bybending at a radius of 10 mm is 0.2 dB/turn or less.
 16. The opticalfiber according to claim 13, wherein the macrobend loss of light havinga wavelength of 1625 nm by bending at a radius of 10 mm is 0.1 dB/turnor less.